Infection diseases induced by various viruses are almost controlled by vaccination, but the prevention of infection due to herpes simplex virus is still a serious problem. In case of first infection in adult, the symptoms are usually very severe, and in developed countries, the population having antibodies against herpes simplex virus (hereinafter, referred to as "HSV") is decreasing. This problem will become more important in future. In some countries, it is considered as a kind of venereal disease or a neonatal herpes infection.
There are two types of virus in HSV, i.e. type 1 and type 2, and the type 1 virus infects mainly around lip, and the type 2 virus infects mainly around genitals.
It is known that both types of viruses are fairly distributed in Japan, and hence, it is important to take effective measures for prophylaxis of the virus infection in future.
Most effective prophylactic measures against virus infections are administration of a vaccine. However, in the case of HSV, development of vaccine is inhibited because of the specific properties of HSV, i.e. carcinogenicity and latent infection of the virus. It is very difficult to confirm that the infectiousness of HSV is removed in a live vaccine prepared from an attenuated virus or in an inactivated vaccine prepared by inactivating the virus by conventional inactivation processes, such as addition of inactivating agents or heat-treatment. If a viral infectiousness is remained in the vaccine, it may induce serious symptom to human body. When such a vaccine is innoculated to human, even though a symptom does not appear immediately, there is a possibility of latent infection. Thus, it is very difficult to prove the safety in HSV vaccine. In other aspect, the vaccine to be used for protection to the infection having low lethal rate such as herpes simplex infection must highly be purified in order to eliminate undesirable side effect. From these viewpoints, the conventional live vaccine and inactivated vaccine are not practically useful.